1. Field of the Invention
This invention relates to apparatus for mixing liquid components with air to form a foam material.
2. Description of the Related Art
Sanitary landfill operators typically cover each day's deposit of garbage with a layer of compacted earth to reduce, among other things, the escape of odors and blowing paper, the proliferation of flies and rodents and excessive leaching of hazardous components from the garbage. The daily earth cover, often about six inches deep, is somewhat expensive to apply due to the use of heavy equipment. The earth cover also occupies a significant volume of the landfill which might otherwise be used for receiving garbage and thus such an earth cover reduces the useful life of the landfill.
Recently, increased interest has been directed toward the use of foamed synthetic materials for covering waste. Typically, such materials are sprayed on the garbage to provide a blanket that, when covered with the next layer of garbage, compresses to occupy relatively little volume. U.S. Pat. Nos. 4,421,788 and 4,519,338, both assigned to the assignee of the present invention, describe apparatus which may be used for applying a foam layer over large areas of landfill in a relatively short time.
An improved foam for landfills is described in U.S. Pat. No. 4,795,764 which is also assigned to the assignee of the present invention. This foam is prepared by mixing aqueous solution of a water-soluble or water-dispersible organic solvent solution of aliphatic isocyanate-terminated prepolymer with an aqueous solution comprising polyamine gelling agent and foaming agents, and incorporating air into this mixture to form a fluid, water-based air foam which is then sprayed onto the exposed surface of a landfill or other substrate. Within a short time period thereafter (for example, within 30 to 60 seconds), the fluid foam gels or stabilizes. Conventionally, the two liquid components of this foam material are mixed in a mixing chamber and then sprayed toward a screen that is located in a compartment. Compressed air is also introduced into the compartment, and the air and mixed liquid materials combine to form the foam material at the screen. The foam material is then discharged through a flattened spreader tip in a fan-shaped pattern.
It has been observed, however, that some pre-gelling of the foam may occur over time on the compartment walls, causing a gradual build-up which eventually restricts the flow of materials through the compartment. Moreover, the gelled materials are occasionally dislodged from the walls and collect on the screen, thus requiring disassembly of the mixing apparatus to unclog the screen. Such a procedure is time consuming and inconvenient.